The effect of UV light and spray drying on glucosamine non-enzymatic browning

Abstract

Non-enzymatic browning reactions, including Maillard and caramelization, are important and complex reactions occurring during food processing and storage. Many factors can affect non- enzymatic browning reactions, which include the concentration of reactants, initial pH, temperature, heating time, water activity, etc. Glucosamine (GlcN) is an amino monosaccharide that contains both an amino group and a carbonyl group. It is capable of undergoing non-enzymatic browning at lower temperatures, generating a plethora of desirable compounds, including α-dicarbonyl compounds (α–DCs), fructosazine (FR) and deoxyfructosazine (DOFR), melanoidins, etc. Among the major α-DCs, 3- deoxyglucosone (3-DG), glucosone (G), methylglyoxal (MGO), glyoxal (GO) and diacetyl (DA) can be generated from GlcN at as low as 25 °C, while increasing the reaction temperature to 37 or 50 °C can speed up this degradation process. MGO, GO, DA, and 3-DG have been reported to have antibacterial activities. Apart from α-DCs, FR and DOFR are the self-condensation products of GlcN. The latter have been reported to have anti-inflammatory properties and are applied in therapeutic uses. At the same time, non-enzymatic browning reactions can generate potential toxic compounds, including 4-methylimidazole (4-MEI), 2-acetyl-4-tetrahydroxybutylimidazole (THI), and 5-hydroxymethylfurfural (5-HMF). The first study aimed to examine the non-enzymatic browning of GlcN under UV-C radiation at 25 °C, referred as “cold caramelization”. Several UV-C exposure times were studied, including 0, 20, 60, 120 min at two GlcN concentrations of 15% and 30%. The physico-chemical properties, quantitation of α-DCs and polyhydroxylalkyl pyrazines (FR and DOFR), alkylimidazoles and 5-hydroxymethylfurfural were determined in all resulting GlcN caramels. The results revealed the possibility of generating GlcN caramel containing desirable compounds by applying UV-C. Specifically, longer UV-C exposure time produced caramel with higher content of G and 3-DG, as well as the GlcN self-condensation products, FR and DOFR. The amount of glucosone was significantly higher compared to GlcN caramels produced under heat treatment. Additionally, none of the neo-formed contaminants were detected during the process. Thus, UV- C treatment may be a newly advantageous method for producing GlcN caramel. The second study focused on the effect of spray-drying on the non-enzymatic browning of GlcN incubated at 50 °C and 90 °C for 12 h. The resulting spray-dried GlcN caramel powders were analyzed along with the non-spray-dried GlcN caramel solutions to compare their physico- chemical properties and concentrations of polyhydroxylalkyl pyrazines, alkylimidazoles, and heterocyclic compounds. Spray-dried GlcN caramels were found to have lower concentrations of both non-volatile FR and DOFR, as well as THI and 5-HMF. In summary, this thesis examined the non-enzymatic browning of GlcN under the application of UV-light and spray-drying, which revealed the possibilities of creating desirable caramels containing bioactive compounds. The resulted caramels can be potentially applied in different food applications.